McClellan, George B(rinton).in full George Brinton McClellan ( born Dec. 3, 1826 , Philadelphia, Pa., U.S.—died Oct. 29, 1885 , Orange, N.J. ) general who skillfully reorganized Union forces in the first year of the American Civil War (1861–65) but drew wide criticism for repeatedly failing to press his advantage over Confederate troops.

Graduating second in his class at the U.S. Military Academy, West Point, N.Y. (1846), McClellan served in the Mexican War (1846–48) and taught military engineering at West Point (1848–51). He was then assigned to conduct a series of surveys for railroad and military installations, concluding with a mission to the Crimea (1855–56) to report on European methods of warfare.

McClellan resigned his commission in 1857 to become chief of engineering for the Illinois Central Railroad and, in 1860, president of the Ohio and Mississippi Railroad. Although a states’ rights Democrat, he was nevertheless a staunch Unionist, and, a month after the outbreak of the American Civil War (April 1861), he was commissioned in the regular army and placed in command of the Department of the Ohio with responsibility for holding western Virginia. By July 13 the Confederate forces there were defeated, and McClellan had established a reputation as the “Young Napoleon of the West.”

After the disastrous Union defeat at the First Battle of Bull Run the same month, McClellan was placed in command of what was to become the Army of the Potomac. He was charged with the defense of the capital and destruction of the enemy’s forces in northern and eastern Virginia. In November he succeeded General Winfield Scott as general in chief of the army. His organizing abilities and logistical understanding brought order out of the chaos of defeat, and he was brilliantly successful in whipping the army into a fighting unit with high morale, efficient staff, and effective supporting services. Yet he refused to take the offensive against the enemy that fall, claiming that the army was not prepared to move. President Abraham Lincoln was disturbed by McClellan’s inactivity and consequently issued his famous General War Order No. 1 (Jan. 27, 1862), calling for the forward movement of all armies. “Little Mac” was able to convince the president that a postponement of two months was desirable and also that the offensive against Richmond should take the route of the peninsula between the York and James rivers in Virginia.

In the Peninsular Campaign (April 4–July 1, 1862), McClellan was never really defeated and actually achieved several victories. But he was overly cautious and seemed reluctant to pursue the enemy. Coming to within a few miles of Richmond, he consistently overestimated the number of troops opposing him, and, when Confederate forces under General Robert E. Lee began an all-out attempt to destroy McClellan’s army in the Seven Days’ Battles (June 25–July 1), McClellan retreated. Lincoln’s discouragement over McClellan’s failure to take Richmond or to defeat the enemy decisively led to the withdrawal of the Army of the Potomac from the peninsula.

Returning to Washington as news of the Union defeat at the Second Battle of Bull Run (August 29–30) was received, McClellan was asked to take command of the army for the defense of the capital. Again exercising his organizing capability, he was able to rejuvenate Union forces. When Lee moved north into Maryland, McClellan’s army stopped the invasion at the Battle of Antietam (September 17). But he again failed to move rapidly to destroy Lee’s army, and, as a result, the exasperated president removed him from command in November.

In 1864 McClellan was nominated for the presidency by the Democratic Party, though he repudiated its platform, denouncing which denounced the war as a failure. On election day he resigned his army commission and later sailed for Europe. Returning in 1868, he served as chief engineer of the New York Department of Docks (1870–72) and in 1872 became president of the Atlantic and Great Western Railroad. He served one term as governor of New Jersey (elected 1877) and spent his remaining years traveling and writing his memoirs.